Michael Bloomberg, U.S.

Donations: $2.8 billion
Net worth: $25 billion
Bloomberg has apparently given to more than 850 charities. He's supported smoking cessation campaigns, tougher national gun control laws and New York's arts institutions. Over the years he's also given $200 million to his alma mater, Johns Hopkins University, where he sits on the board. In 2011, he donated $330 million to such groups as the Sierra Club, the Alliance for the Arts and the American Foundation for Suicide Prevention.